Rotary connector having and identifiable neutral position

ABSTRACT

A rotary connector includes a first part, a second part configured to rotate relative to the first part, and an electrical cable housed within the rotary connector. A viewing window is configured to reveal a feature of the electrical cable when the rotary connector is in a neutral position.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a rotary connector, and particularly to a rotary connector having an alignment feature and/or an overcurrent protection feature.

[0003] 2. Discussion of the Background:

[0004] A rotary connector is used as a connector device for a flexible transmission medium that transfers electrical signals, optical signals, electric power, etc. between a stationary member and a rotating member rotating relatively to the stationary member within a limited range of rotational number. In this rotary connector, a flexible flat cable is housed in the form of a spiral connector within an annular space defined by a rotating case and a stationary case, which are combined for rotation. Alternatively, U.S. Pat. No. 5,310,356 assigned to The Furukawa Electric Co., Ltd discloses a flexible flat cable is housed in a rotary case in the form of stationary windings along the inside wall of the stationary member, then reversing direction via a U-shape turn, and continuing as rotating windings along the outside wall of the rotational member. The entire contents of U.S. Pat. No. 5,310,356 are incorporated herein by reference. Opposing ends of the flexible flat cable are connected to the rotating case and stationary case respectively, and the rotating case is allowed to rotate relatively to the stationary case as the flat cable is coiled and uncoiled simultaneously from the respective side walls of the rotary connector.

[0005] The rotary connector is typically required to be in a neutral position when mounted in a final assembly. The neutral position is usually a center position in the range of rotational movement of the rotary connector so that the rotary connector can be rotated the same number of rotations (i.e. angular rotational range) in both the clockwise and counterclockwise direction without damaging the flexible flat cable fixed to the stationary and rotary part of the rotary connector. That is, the neutral position allows the same number of functional rotations in either direction. In mounting the rotary connector in the steering apparatus of an automobile, for example, the steering wheel is adjusted to a straight-advance position as the neutral position connector is set into the steering apparatus. Thus, the steering wheel is free to operate the steering apparatus without causing a strain (or breaking) the flexible flat cable.

[0006] Because the rotary connector is provided as a subcomponent of a final assembly, such as a steering wheel assembly, the rotary connector is typically fixed in the neutral position until placed in the final assembly, where the rotary connector is made free to rotate in the assembly. Fixing in the neutral position is typically provided by a fixing pin having retaining hooks, called snap fits, that are removably mounted extending between mounting portions on the rotating and stationary cases, or by a seal that is pasted on both the cases. An example of a fixing mechanism is disclosed in U.S. Pat. No. 5,257,943, the entire content of which is incorporated herein by reference.

[0007] Conventional methods of fixing or sealing the rotary connector are problematic, however, in that it is difficult to verify that the connector is actually in the neutral position at the time of assembly. While the rotational and stationary part of the connector may have alignment marks that indicate the relative position of these parts when they are in the neutral position, because the rotational connector can make several complete rotations, the alignment marks may be aligned in positions other than the neutral position. Therefore, if the fixed or sealed neutral position is broken during transport of the rotary connector to the place of final assembly, for example, the neutral position cannot be found by using the alignment marks. Moreover, even if the fixed or sealed neutral position is not broken, it cannot be visually verified at final assembly that the rotary connector is actually in the alignment position corresponding to the neutral position.

[0008] Over current protection for the flexible flat cable has conventionally been provided by a fuse housed in a fuse box mounted on the final assembly such as a vehicle chassis. Such a fuse box is typically bulky and requires additional wiring from the rotary connector, which leads to additional material and assembly cost. Moreover, the fuse box may be accessible to an inexperienced user of the final assembly, which may lead to the wrong fuse being provided in the fuse box. Where the replaced fuse is rated lower than the proper fuse rating, premature blowing of the fuse may occur. More importantly, where the replaced fuse is rated higher than the proper fuse rating, excessive heat and even fire may result.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to mitigate any or all of the above-described problems.

[0010] Another object of the present invention is to provide a rotary connector that allows simple verification of a neutral position of the rotary connector.

[0011] Yet another object of the present invention is to provide a rotary connector having a simple and compact overcurrent protection feature.

[0012] These and other objects of the present invention are provided by a rotary connector. According to one aspect of the invention the rotary connector includes a first part, a second part configured to rotate relative to the first part, and an electrical cable housed within the rotary connector. A viewing window is configured to reveal a feature of the electrical cable when the rotary connector is in a neutral position.

[0013] In another aspect of the invention a steering wheel assembly includes a rotary connector including a first part, a second part configured to rotate relative to the first part, and an electrical cable housed within the rotary connector. A viewing window is configured to reveal a feature of the electrical cable when the rotary connector is in a neutral position.

[0014] In still another aspect of the invention, a method of manufacturing a rotary connector includes providing first and second parts of the rotary connector that can be rotationally coupled to one another, and providing a flexible cable that can be housed within the rotary connector when the first and second parts are rotationally coupled to one another. The flexible cable in a predetermined arrangement within the rotationally coupled first and second parts such that a feature of the flexible cable is visible from an exterior of the rotary connector when the first part is in a neutral position relative to the second part.

[0015] Another aspect of the invention includes a rotary connector includes a stationary case, a rotating case configured to rotate relative to the stationary case, an electrical cable housed within the rotary connector, and means for indicating a neutral position of the rotary connector.

[0016] Still another aspect of the invention is a method of identifying a neutral position of a rotary connector. The method includes rotating a first part of the connector relative to a second part of the connector such that through holes in the first and second part are substantially aligned to reveal an interior annular space of the rotary connector. The first and second parts of the connector are positioned such that a feature of an electrical cable housed in the interior annular space is visible to indicate a neutral position of the rotary connector.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0018]FIG. 1 is a perspective view of a rotary connector in accordance with one embodiment of the present invention;

[0019]FIG. 2 is a partial cross-sectional view taken along line A-A of FIG. 1;

[0020]FIG. 3 is an exploded view of the rotary connector showing the interrelation of parts included in a rotary connector assembly according to one embodiment of the present invention;

[0021]FIG. 4 is an illustration of a flexible flat cable assembly used with the a rotary connector in accordance with one embodiment of the present invention;

[0022]FIGS. 5-7 are illustrations showing various constructions of a flexible flat cable that may be used in accordance with the present invention;

[0023]FIGS. 8a and 8 b are front views of the rotary connector 1 that illustrate the use of viewing window and U-shaped bend 20 c to indicate a neutral position of the rotary connector, in accordance with one embodiment of the present invention;

[0024]FIG. 9 shows a multiple conductor flexible flat cable used in prior art rotary connectors;

[0025]FIG. 10 shows a single ribbon flexible flat cable used in accordance with an embodiment of the present invention;

[0026]FIG. 11 is a drawing of a high current capable rotary connector having an integral blade fuse in accordance with one embodiment of the present invention;

[0027]FIG. 12 is an enlarged drawing showing details of the blade fuse area of the rotary connector in accordance with one embodiment of the present invention;

[0028]FIG. 13A is a drawing showing the configuration of a prior art bus bar assembly;

[0029]FIG. 13B is a drawing showing the configuration of a bus bar assembly in accordance with an embodiment of the present invention;

[0030]FIG. 14 is a drawing showing a detailed configuration of a bus bar assembly having a surface mount fuse in accordance with one embodiment of the present invention; and

[0031]FIG. 15 is a drawing showing a detailed configuration of a bus bar assembly having a Pico fuse in accordance with one embodiment of the present.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Referring now to the drawings, FIG. 1 is a perspective view of a rotary connector in accordance with one embodiment of the present invention, and FIG. 2 is a partial cross-sectional view taken along line A-A of FIG. 1. As seen in FIG. 1, the rotary connector 1 includes a rotating case 10 and a stationary case 11. The rotating case 10 includes an inner cylinder shaft portion 10 a and an upper flange 10 b. The upper flange 10 b includes a rotating junction 10 c, which provides electrical connection of a cable (not shown in FIG. 1) housed in the connector to an external electrical system. In the embodiment of FIG. 1, the rotating junction 10 c includes wires 12, however pins may also be used. The upper flange 10 b of the rotating case 10 further includes a through hole 10 d positioned at a predetermined radial position on the upper flange 10 b.

[0033] As best seen in FIG. 2, the stationary case 11 includes an outer cylinder wall 11 a, an upper flange 11 b and a lower flange 11 c. The upper flange 11 b is provided with a through hole 11 d. The through hole 11 d is positioned at substantially the same radial position as the through hole 10 d so that these through holes overlap one another when rotated to the same angular position. Overlapping of the through holes 10 d and 11 d creates a window 1 a that allows visual indication of a flexible flat cable within an annular space of the rotary connector 1 as will be further described below. Referring again to FIG. 1, the stationary case 11 includes a plurality of mounting flanges 11 e arranged at suitable positions on the outer cylinder wall 11 a for fixedly mounting the stationary case 11 on an assembly such as a vehicle-body. Also arranged on the outer cylinder wall 11 a of the case 11 is a stationary junction 11 f, which provides electrical connection of the cable housed in the rotary connector 1 to an external electrical system. In the embodiment of FIG. 1, the stationary junction 11 f includes wires 13, however, pins may also be used.

[0034]FIG. 3 is an exploded view of the rotary connector showing the interrelation of parts included in a rotary connector assembly according to one embodiment of the present invention. As seen in this figure, the rotary connector assembly includes a rotating case 310, a stationary case 311, a flexible flat cable 320 and a separable stationary flange 311 c. The rotating case 310 includes a rotating junction 310 c and the stationary case 311 includes a stationary junction 311 f. As seen in FIG. 3, the flexible flat cable 320 includes four separate flat cables bent to form U-shapes 320 c. The stationary case 311 joins with the stationary flange 311 c along the dashed assembly line in FIG. 3 to form an integral unit defining an annular space that the flexible flat cable 320 is contained in. The rotating case 310 is then rotationally coupled to the stationary case 311. As with the embodiment of FIGS. 1 and 2, the rotating case 310 and the stationary case 311 include a rotating through hole 310 c and a stationary through hole 311 d respectively. The through hole 311 d is positioned at substantially the same radial position as the through hole 310 c so that they overlap one another when rotated to the same angular position. While not shown in FIG. 3, in the final assembly of the rotary connector, one end of the flexible flat cable 320 is connected to the rotating junction 310 c of the rotating case 310, and an opposing end of the cable 320 is connected to the stationary junction 311 f of the stationary case 311.

[0035]FIG. 4 is an illustration of a flexible flat cable assembly used with a rotational connector in accordance with one embodiment of the present invention. One end of the flexible flat cable 420 includes rotational junction 410 d having male pins 412, while an opposing end of the flexible flat cable 420 includes stationary junction 411 f having male wires or pins or wires 413. In the embodiment of FIG. 4, the male pins or wires 412 and 413 are suitable for connecting the flexible flat cable 420 to female electrical connectors of external wires. As with the embodiment of FIG. 3, the flexible flat cable 420 of FIG. 4 includes four flat wires that are housed within the annular space of the rotary connector. However, it is understood that the number of flat wires in the cable assembly may be changed depending on the electrical requirements of the assembly that the flexible flat cable is used with. Moreover, in one embodiment of the present invention, the rotary connector has a fixed number of flat wires, with a predetermined number of flat wires being electrically active based on the electrical requirements of the assembly, and remaining cables being “dummy cables” that act as spacers.

[0036] As seen in FIG. 4, the flat wires of the flexible flat cable 420 are housed such that each wire has some of its length wrapped around the inner cylinder shaft portion 10 a of the rotating case 10 shown in FIG. 1, for example. Each wire of the flat cable 420 is then turned back upon itself to form a U-shape 420 c so that the remainder of the flexible flat cable length is wound inside the outer cylinder wall 11 a of the stationary case 11 in an opposite direction. The U-shape bend 420 c of one of the flat wires of the flexible flat cable 420 acts as an indicator that the rotary cable is in a neutral position as will be further described below.

[0037] The flat cable of FIGS. 3 and 4 is a flexible belt-shaped transmission medium for transmitting electrical signals, optical signals, electric power, etc. As shown in FIG. 5, for example, the cable 520 is an electrical transmission medium that includes a plurality of flat rectangular electrical conductors 520 a, arranged parallel to one another. In the embodiment of FIG. 5, an insulator 520 b, such as a polyester film, covers the conductors 520 a to electrically insulate them from one another. FIGS. 6 and 7 show alternative constructions of a flexible flat cable that may be used in accordance with the present invention. As seen in FIG. 6, a cable 620 is an electrical transmission medium that includes a plurality of electrical conductors 620 a, having a circular cross section and arranged parallel to one another. An electrical insulation material 620 b covers the conductors 620 a. In FIG. 7, a flat cable 720 is a light transmission medium in the form of a tape fiber that includes a plurality of optical fibers 720 a for transmitting optical signals. A covering material 720 b covers the fibers 720 a and provides a flexibility to the cable. Still alternatively, the flat cable may be a combination of an electrical transmission medium and a light transmission medium, in which case the cable includes electrical conductors and optical fibers covered by an insulation material. In one embodiment of the present invention, a single conductor ribbon wire may be used for the flexible flat cable, as will be described with respect to FIG. 10 below.

[0038] As noted above, viewing of the U-shaped bend of the flexible flat cable within the window provides an indication that the rotary connector is in a desired neutral position. FIGS. 8a and 8 b are front views of a rotary connector 1 that illustrate the use of viewing window and the U-shaped bend to indicate a neutral position of the rotary connector, in accordance with one embodiment of the present invention. In FIGS. 8a and 8 b, the rotary connector 801 is positioned such that the through hole of the rotating case overlaps the through hole of the stationary case to form viewing window 801 a that allows viewing of the interior annular space of the rotary connector 801.

[0039] As seen in FIG. 8a, there is no flat cable bend visible within the viewing window 801 a, which indicates that the rotary connector 801 is not in its neutral position. That is, the rotary case is in a position relative to the stationary case, other than the neutral position. While FIG. 8a shows no visibility of the flexible cable 820 in the window 1 a, one of ordinary skill in the art would understand that a portion of the cable 20 other than the U-shaped bend 20 c may be visible in the viewing window 801 a. In such a situation an orientation of the cable 820 will make clear that the portion of the cable 820 in the window 801 is not the bend 820 c, and therefore, the rotary connector is not in its neutral position. However, where the rotary case is rotated relative to the stationary case such that the U-shaped bend 820 c is within the viewing window 801 a, the rotary connector 801 is in the neutral position as shown in FIG. 8b.

[0040] Thus, according to the present invention, the rotating case 10 is in a neutral position relative to the stationary case 11 when the through holes 10 d and 11 d are aligned to form viewing window 1 a, and one of the U-shaped bends 20 c of the cable 20 is visible within the viewing window 1 a. In order for the alignment of the viewing window 1 a and the cable bend 20 c to correspond to the neutral position, the through holes 10 d and 11 d must be positioned in a predetermined position on the rotary connector, and the length of the flexible flat cable 20 must correspond to the positioning of the viewing window 1 a as well as the rotational range (i.e. the maximum number of turns or angular rotation) of the rotary connector. That is, where the rotary connector 1 has a rotational range of several turns, the viewing window will appear with each 360 degrees of rotation, but the length of the flexible flat cable 20 is selected such that a bend 20 c will appear in the viewing window only when the connector is in the desired neutral position.

[0041] For example, in the embodiment of the present invention shown in FIG. 3, the flexible flat cable 320 is 805 mm long and the viewing window formed by the through holes 210 d and 311 d is located at approximately 2 o'clock when referenced to a clock face, if viewed from the vehicle driver's position in the case of an automobile application. With this configuration, the rotary connector will have a rotational range of approximately +/−2.5 turns and the cable bend 320 c will appear in the viewing window at approximately 2.5 turns from each end of the functional rotational range. This identifies the functional center of the rotary connector and the neutral position. It is to be understood, however, that the present invention is not limited to this specific example, and the rotational range of the connector may be any number of turns with the desired neutral position being other than the functional center of the connector.

[0042] More specifically, in one embodiment of the present invention, the cable lengths L₁, L₂, L₃ and L₄ of the present invention have four progressively longer lengths. The cable lengths may be determined by the following calculations:

L ₁=*length to make bus bar (rotor side)+(2.5)(π)(d _(r))+(0.5)(π)((d _(s) −d _(r))/2)+(2.5)(π)(d _(s))+*length to make bus bar (stationary side).

L ₂=*length to make bus bar (rotor side)+(2.75)(π)(d _(r))+(0.5)(π)((d _(s) −d _(r))/2)+(2.75)(π)(d _(s))+*length to make bus bar (stationary side).

L ₃=*length to make bus bar (rotor side)+(3)(π)(d _(r))+(0.5)(π)((d _(s) −d _(r))/2)+(3)(π)(d _(s))+*length to make bus bar (stationary side).

L ₄=*length to make bus bar (rotor side)+(3.25)(π)(d _(r))+(0.5)(π)((d _(s) −d _(r))/2)+(3.25)(π)(d _(s))+*length to make bus bar (stationary side).

[0043] Where:

[0044] *length varies due to external design factors

[0045] d_(r)=outside diameter of rotational member

[0046] d_(s)=inside diameter of stationary member]

[0047] In addition, the calculation of cable lengths may account for the thickness of the cable. Referring to FIG. 4, the distance from the outer circle of the cables to the stationary junction 411 f and the distance from the inner circle to the rotating junction 410 d are the “lengths to make bus bar”. These distances can vary from design to design and cannot be formulated as with the diameters.

[0048] Centering of the rotary connector to a neutral position will be described with respect to the rotary connector 1 shown in FIG. 1. Centering to the neutral position is preferably accomplished by turning the rotary case 10 in a clockwise direction. Rotation is complete when the rotary connector 1 has depleted the flat cable 20 windings along the inner wall 11 a of the stationary case 11 and begins to pull at the junction 11 f. The pulling of the flat cable 20, at the stationary junction 11 f is readily discernable as the operating torque of the rotary connector 1 is very low (typically <0.1 Nm) and the end of travel for the flat cable 20 feels much like the rotary connector 1 has been snagged. Once the end of rotational travel has been established, the rotating case 10 is to be counter-rotated (2.5-3.0 turns in a preferred embodiment) until the through hole 10 d of the rotating case 10 aligns with the through hole 11 d of the stationary case 11, creating a centering window 1 a. When the U-shape turn 20 c of the flat cable 20 appears in the centering window 1 a the rotary connector 1 is properly centered within its functional rotational limits, i.e. its neutral position.

[0049] In one embodiment of the present invention, the rotary connector may be provided with a fixing mechanism such as that described in U.S. Pat. No. 5,257,943, which is incorporated herein by reference. In accordance with the present invention however, if the fixing mechanism for fixing the rotary connector in a neutral position is broken during transport of the rotary connector to the final assembly, the neutral position can be easily found at the place of final assembly. Moreover, the fixing mechanism may be eliminated from the rotary connector to save material and assembly costs. Finally viewing the U-shaped bend at the flexible flat cable in the viewing window provides visual assurance at the final assembly that the rotary connector is actually in a neutral position.

[0050] In one embodiment of a rotary connector, the flexible cable within the connector may require overcurrent protection. As noted in the background section above, prior art rotary connectors provided such overcurrent protection by a fuse contained in a separate fuse box that was bulky and unsightly, and readily accessible to any user of the assembly that the rotary connector was applied to. The present inventors recognized that the need for housing the fuse in an external fuse box was due to space considerations within the rotary connector. More specifically, the present inventors discovered that the prior art use of multiple conductor flexible flat cables to provide high current capability required the use of multiple fuses to provide overcurrent protection of the cable.

[0051]FIG. 9 shows a multiple conductor flexible flat cable typically used in prior art rotary connectors. As seen in this figure, the prior art cable includes input bus bar 901, input cable length 903, input bus bar 905, load 907, output bus bar 909, output cable length 911, and output bus bar 913. The input components, 901, 903 and 905 carry current to the load 907, and the output components 909, 911, and 913 carry current away from the load 907. For example, the input components may carry high current from chassis wires of an automobile to a resistive heating coil of a heated steering wheel in an automobile, while the output components provide current to return wires in the chassis of the automobile.

[0052] As seen in FIG. 9, each of the input length 903 and the output length 911 include six conductors 915 separated from one another by insulation strips 917. The input bus bar 905 and output bus bar 909 each provide a common electrical connection for the six conductors 915 of their respective connectors in order to provide high current to the load 907. However, the input bus bar 901 and the output bus bar 913 provide six discrete bonding pads for chassis wires that carry current to and from the flexible flat cable. As also seen in FIG. 9, use of the discrete bus bars 901 and 913 require six different fuses 920 to provide overcurrent protection for each of the six current paths providing current to the load 907. The present inventors recognized that this configuration results in inefficient use of space that prevents the overcurrent protection system of the flexible flat cable from being provided integral with the rotary connector.

[0053]FIG. 10 shows a single ribbon flexible flat cable used in accordance with an embodiment of the present invention. As seen in this figure, the cable includes input bus bar 1001, input cable length 1003, input bus bar 1005, load 1007, output bus bar 1009, output cable length 1011, and output bus bar 1013. As with the prior art cable of FIG. 9, the input components, 1001, 1003 and 1005 carry current to the load 1007, and the output components 1009, 1011, and 1013 carry current away from the load 1007. However, as seen in FIG. 10, each of the input length 1003 and the output length 1011 includes a single ribbon conductor 1015 having a relatively large width for providing high current capacity. The single ribbon conductor is preferably made of copper, but any suitable conductor may be used. The ribbon conductors 1015 are coated with an insulating material such as a mylar sheet that electrically insulates and provides a flexibility for the cable lengths. Because the cable lengths 1003 and 1011 use a single ribbon conductor, each of the bus bars 1001, 1005, 1009, and 1013 are common electrical connection bus bars. Thus, as also seen in FIG. 10, a single fuse 1020 provides overcurrent protection for the flexible flat cable. The present inventors recognized that such use of a single fuse provides space efficiency that allows the overcurrent protection to be integrated within the rotary connector.

[0054]FIG. 11 is a picture of a high current capable rotary connector having an integral blade fuse in accordance with one embodiment of the present invention. As seen in FIG. 11, the rotary connector 1101 is shown without a cover to reveal the flexible flat cables housed within the annular space of the rotary connector 1101. The rotary connector 1101 includes a rotating case and a stationary case, combined for the purpose of housing flexible flat cable(s), similar to the rotary connectors previously described with respect to FIGS. 1 and 4. In the embodiment of FIG. 11, the flexible flat cable 1120 includes four flat wires, two of which are single conductor ribbon wires (1103 visible in FIG. 11) for providing input and output high current to the rotary connector 1101, with the two remaining ribbon wires being multiple conductor wires (1105 visible in FIG. 11) for providing separate current sources to the rotary cable 1101. While the flexible flat cable 1120 of FIG. 11 is shown to have U-shaped turns 1120 c, such a configuration is not necessary to obtaining the advantages of the overcurrent fuse provided integral to the rotary connector 1101. For example, the flexible flat cable 1120 may be provided as a spiral, as described for prior art cables in the Background of the Invention section above.

[0055] The ribbon wires of the flexible cable 1120 are coated with a Mylar sheet and electrically connected with a bus-bar to the rotating and stationary mating terminations of the rotary connector. The Mylar sheet affords some structure to the flat cable and provides electrical insulation from adjacent flat cables. By design, these flat cables are incapable of handling currents exceeding a predetermined amperage (for example 8.0 Amps), so over-current protection is generally necessary. In FIG. 11, the over current protection is provided by a blade fuse 1107 mounted internal to the rotary connector 1101. The blade fuse 1107 is suitably rated for the size of the copper ribbon and preferably snaps into a recess in the rotary connector 1101 so as to be completely housed within the rotary connector 1101 when the connector is fully assembled.

[0056]FIG. 12 is an enlarged drawing showing details of a blade fuse area of a rotary connector in accordance with one embodiment of the present invention. As seen in this figure, the electrical bus-bar of the present invention is separated into two electrically insulated parts 1203 and 1205. Each insulated side 1203 and 1205 of the bus bar includes tangs (not shown) that protrude and provide a suitable docking feature for intermediate terminals 1209 which in turn provide a suitable docking feature the blade type fuse 1207. The bus-bar also serves as an intermediate terminal for electrically fixing the flexible flat cable to any external wires.

[0057] In addition to providing a fuse contained within the rotary connector, a bus bar assembly according to the present invention provides heat sinking features that improve the over current protection for the flexible flat cable of the rotary connector. FIG. 13A is a drawing showing the configuration of a prior art bus bar assembly. As seen in this figure, the prior art bus bar assembly of includes a housing 1351 and six discrete bonding pads 1353 for connecting discrete wires to the bus bar assembly as described with respect to FIG. 9 above. The bonding pads 1353 of the bus-bar assembly are fabricated using a nominal copper thickness of 0.3 mm appropriate for ultra sonic welding of the flexible flat cable and round wire to the bus bar. The present inventors have recognized that this configuration of the prior art bus bar assembly provides little ability to sink away excess heat created by high current electrical loads, thus potentially blowing the fuse prematurely.

[0058]FIG. 13B is a drawing showing the configuration of a bus bar assembly in accordance with an embodiment of the present invention. As seen in this figure, the bus bar assembly includes a housing 1301, and parts 1303 and 1305 physically separated and electrically insulated from one another. While not shown in FIG. 13A, the parts 1303 and 1305 are electrically connected to one another by a fuse device that provides over current protection for the rotary cable assembly. As shown in FIG. 13B, the bus-bar parts 1303 and 1305 are fabricated using extra thick copper of 0.8 mm, which sinks away some of the heat created from high electrical loads, thus avoiding premature fuse blow. Moreover, the housing 1301 of the bus bar assembly includes sink fins 1309 that sink away some of the heat created from high current electrical loads, thus avoiding premature fuse blow. While not shown in FIG. 13B, the housing 1301 may also include a cooling pipe for heat sinking. In the embodiment of FIG. 13B, the housing 1301 includes a wire recess 1311 for holding an input round wire, such as a chassis wire of an automobile, to the bus bar assembly, and a bus bar connector portion 1313 for connecting to a connector end of the flexible flat cable of the rotary connector.

[0059]FIG. 14 is a drawing showing a detailed configuration of a bus bar assembly having a surface mount fuse in accordance with one embodiment of the present invention. As with the bus bar described in FIG. 12, the bus bar includes a housing 1401 and electrically insulated parts 1403 and 1405. The parts 1403 and 1405 are electrically connected by surface mount fuse 1407. In addition, the bus bar assembly includes heating fins 1409 and increased thickness copper. The bus bar and fuse assembly also includes a round wire recess 1411 for holding an input wire to the bus bar assembly, and a bus bar connector portion 1413 for connecting to a connector end of the flexible flat cable of the rotary connector. FIG. 15 is a drawing showing a detailed configuration of a bus bar assembly having a Pico fuse in accordance with one embodiment of the present. As with the embodiments previously described, the bus bar assembly includes a housing 1501 and electrically insulated parts 1503 and 1505. In the embodiment of FIG. 15, each insulated side of the bus bar 1503 and 1505 has a hole that provides typical mounting for Pico fuse 1507, which electrically connects the parts 1503 and 1505. The bus bar assembly of FIG. 15 also includes heating fins 1509 and increased thickness copper. FIG. 15 also shows an electrical wire fixed in the wire recess 1509, and a ribbon cable fixed to the bus bar connector portion 1511.

[0060] Thus, a rotary connector of the present invention houses a fused devise for purpose protecting vulnerable flexible flat cables from over-current loading. The fused device is preferably housed within the connector in a more overall compact design of the rotary connector. Moreover, the fused device is preferably housed within the connector such a way as to not permit replacement of the fuse so that the rotary connector is provided as a replacement unit. However, an embodiment of the invention may include a fuse provided integral to the rotary connector and readily removable for replacement by any user, or by use of special purpose tooling that is generally available only to experienced maintenance persons.

[0061] Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

1. A rotary connector comprising a first part; a second part configured to rotate relative to said first part; an electrical cable housed within the rotary connector; and a viewing window configured to reveal a feature of said electrical cable when the rotary connector is in a neutral position.
 2. The rotary connector of claim 1, wherein said first part is a stationary case and said second part is a rotary case.
 3. The rotary connector of claim 2, wherein said viewing window comprises: a first through hole positioned at a predetermined position on said rotating case; and a second through hole positioned at a predetermined position in said stationary case such that the first and second through holes overlap to reveal an interior annular space of the connector that said electrical cable is housed within when the rotating case is rotated with respect to the stationary case, wherein said feature of the electrical cable comprises a unshaped bend that occupies the overlapping area of the first and second through holes when said rotary connector is in said neutral position.
 4. The rotary connector of claim 3, wherein said rotating case and said stationary case have substantially the same axis of rotation and said first and second through holes have substantially the same radial position with respect to the axis.
 5. The rotary connector of claim 2, further comprising an electrical junction configured to provide electrical connection between the electrical cable and an external unit.
 6. The rotary connector of claim 5, wherein said electrical junction comprises pins.
 7. The rotary connector of claim 5, wherein said electrical junction comprises wires.
 8. The rotary connector of claim 5, wherein said electrical junction comprises a rotating junction coupled to said rotating case.
 9. The rotary connector of claim 5, wherein said electrical junction comprises a stationary junction coupled to said stationary case.
 10. The rotary connector of claim 2, wherein said stationary case comprises mounting tabs configured to mount said rotary connector to an assembly.
 11. The rotary connector of claim 2, wherein said electrical cable comprises an electrical conductor embedded in an insulating material.
 12. The rotary connector of claim 2, wherein said electrical cable comprises an optical signal transmission line.
 13. The rotary connector of claim 2, wherein said electrical cable comprises a plurality of flexible flat cables.
 14. The rotary connector of claim 2, wherein said stationary case comprises: a lower flange and a stationary upper flange opposing said lower flange; and an outer cylinder wall connecting said lower and stationary upper flanges, said stationary upper flange having a stationary through hole positioned at a predetermined radial and angular positions.
 15. The rotary connector of claim 14, wherein said rotating case comprises; an inner cylinder shaft portion; and a rotating upper flange overlapping the stationary upper flange of said stationary case when said rotating case is rotationally coupled to said stationary case, said rotating upper flange having a rotating through hole that overlaps said stationary through hole when the rotating case is positioned at a predetermined position relative to said stationary case.
 16. The rotary connector of claim 15, wherein said inner cylinder shaft portion opposes said outer cylinder wall, and said upper stationary flange opposes said lower flange to form an annular space within said connector when said rotating case is rotationally coupled to said stationary case.
 17. The rotary connector of claim 16, wherein said electrical cable comprises a flexible flat cable having a first portion of its length wrapped around the inner cylinder shaft portion of the rotating case in a first direction, the flat cable then being turned back upon itself to form a U-shape so that a second portion flexible flat cable length is wound inside the outer cylinder wall of the stationary case in an opposite direction to the first direction.
 18. The rotary connector of claim 17, wherein said first and second portions of said flexible flat cable have predetermined lengths that ensure that the U-shape bend of the flexible flat cable is visible within an overlapping area of the windows when the rotary connector is in said neutral position.
 19. The rotary connector of claim 1, wherein said viewing window is configured to reveal a feature of said electrical cable only when the rotary connector is in a neutral position.
 20. The rotary connector of claim 1, wherein said rotary connector does not include an indication arrow for indicating said neutral position.
 21. A steering wheel assembly comprising a rotary connector as claimed in any one of claims 1-20.
 22. A method of manufacturing a rotary connector, comprising: providing first and second parts of the rotary connector that can be rotationally coupled to one another; providing a flexible cable that can be housed within the rotary connector when the first and second parts are rotationally coupled to one another; and arranging the flexible cable in a predetermined arrangement within the rotationally coupled first and second parts such that a feature of the flexible cable is visible from an exterior of the rotary connector when the first part is in a neutral position relative to the second part.
 23. The method of claim 22, wherein said arranging the flexible cable comprises arranging the flexible cable to form a U-shaped bend as said feature.
 24. A rotary connector comprising a stationary case; a rotating case configured to rotate relative to the stationary case; an electrical cable housed within the rotary connector; and means for indicating a neutral position of the rotary connector.
 25. A method of identifying a neutral position of a rotary connector, comprising: rotating a first part of the connector relative to a second part of the connector such that through holes in the first and second part are substantially aligned to reveal an interior annular space of the rotary connector; and positioning the first and second parts of the connector such that a feature of an electrical cable housed in the interior annular space is visible to indicate a neutral position of said rotary connector. 